1. Field of the Invention
The present invention relates to a generator for a wind power installation. The generator has teeth which are surrounded by windings and separated by slots, and permanent magnets that form the poles of the exciter field.
2. Description of the Related Art
An important goal of the further development of wind power installations is reduction of the noise produced by their operation. A high noise level is produced above all when the tower or other parts of the plant are excited with their natural frequency. Therefore, to control noise, it is primarily necessary to prevent vibrational excitations.
One of the causes of noise can be the meshing of the teeth in a transmission transmitting the rotation of the rotor to a generator. But the generator is also a source of vibrational excitations. The principal cause of this is so-called slot cogging torques. A well-known means of suppressing slot cogging torques is oblique arrangement of the poles and/or teeth.
EP 0 995 257 B1 discloses a wind power installation, in which noise is reduced by using a synchronous generator, whose rotor carries n poles, which are arranged asymmetrically with respect to a plane that contains the axis of rotation of the rotor. Other measures for reducing local vibrational excitations in the generator consist in a pole geometry with the shape of an arrowhead and in pole pieces designed with a trapezoidal cross section.